Picture of the Moment...

Comet 17P Holmes, the exploding comet, 31 October 2007

Comet 17P/Holmes exploded on 25 October 2007, sending a cloud of debris into space and increasing it's brightness by a million times. This transformed it from an object requiring a large telescope to see into a second magnitude star, rivalling those in its host constellation - Perseus.

Images 1 to 3 of the above montage show Holmes, the Pleiades star cluster and the Moon all photographed at the same scale on the same night. The 4th picture is a larger view of the comet on the same evening, 31 October 2007.

As the cloud expanded around 2km per second so it came to look less like a star and more like a comet. Because of the great distance of around 200 million km, the expansion was too slow to watch in real time but was quite evident from night to night.

The cause of the explosion is unclear, though the most likely explanations are a collapsing void in the nucleus as it evaporated due to heating by the sun or a collision with companion piece of nucleus . This is the second recorded such event on Holmes, the first in 1892 being the one that lead to the comet's discovery.

Click the image or here for more of the story and to see how the comet grew in the following weeks.

Picture added on 30 Nov 2007

Previous Moments...

Total Lunar Eclipse:A clear night allowed a complete view from start to finish, 3 - 4 March 2007
Comet McNaught C/2006 P1: The brightest comet in a generation, January 2007
Harvest Moon Eclipse: Only a partial eclipse but still a wonderful sight rising over the hills of Kent, 7 Sept 2006
Noctilucent Clouds: Ice crystals on the very edge of space, 14 July 2006
Dark Sun over the Sahara: A spectacular total eclipse of the Sun seen from the Libyan desert, 29 March 2006
Ring of Fire: An annular eclipse of the Sun over Spain, 3 Oct 2005
A Southern Hemisphere Lunar Eclipse: A total eclipse seen from Argentina, 28 - 29 Oct 2004
Transit of Venus across the Sun: The first for 122 years, 8 June 2004
A Quick tour of the Solar System: Four planets and three moons, 9 April 2004
Fireworks Eclipse of the Moon: A total eclipse on fireworks night, 9 Nov 2003
Sunstorm: Three huge sunspots cause havoc, and wonderful aurorae (for those with clear skies), 27 Oct 2003
Mars: closest approach to Earth in 60,000 years, 30 Aug 2003
Ring of Brodgar, Orkney Islands: An ancient stone circle in a barren northern land, 8 Jun 2003
Mercury Transit: The planet Mercury caught in a rare transit across the face of the Sun, 7 May 2003
Diamond Ring: a short but stunning total solar eclipse in the Australian Outback, 4 Dec 2002
Concrete Cows in Milton Keynes, 16 Aug 2002
International Space Station passes over Hay on Wye, 4 June 2002